The invention relates to a vessel comprising a turret extending vertically within the hull of the vessel, the turret having a cylindrical turret wall with an upper part and a lower part and an annular attachment element which is rotatingly connected to the lower part of the turret wall for the connection of one or more anchor lines for mooring the vessel to the sea bed, the lower part of the turret wall being located at or near keel level, wherein the upper part of the turret wall is located at a position which is below the level halfway between deck level and keel level.
From U.S. Pat. No. 5,266,061 a vessel is known comprising a large diameter turret wall that extends from deck level vertically downwards into a moon pool located near keel level. Within the fixed turret wall, a lower turret section is rotatingly connected. The lower turret section comprises a chain table which is connected to the sea-bed in a geostationary manner. Risers, which extend from a sub-sea structure such as a well head, enter the turret through the chain table and extend into a central shaft extending up to deck level, the central shaft being rotatable together with the chain table within the turret wall. During weathervaning of the vessel, the outer turret wall will rotate together with the vessel around the geostationary chain table, the lower part of the turret and the central shaft accommodating the product pipes.
Providing a large diameter turret wall inside the vessel, the diameter of which may amount up to between 15 and 20 meters, is an extensive operation which may cause a structural weakening of the vessel and which requires separate reinforcements. Futhermore, once a vessel is provided with such a large turret construction for conversion of a tanker to a floating production, storage and offloading vessel (FPSO), it can not easily be rebuilt and brought back into its original state as a transport tanker.
From U.S. Pat. No. 5,237,948 a vessel is known comprising a mooring system. Herein the chain table is fixed to a rigid shaft connected to the hull of the vessel. The chain table is rotatably supported on a flange on the shaft. This construction has as a disadvantage that the known chain table will be susceptible to bending moments which can be directly transferred to the bearings.